Its all a red herring

David is not the shooter. This show is far too grounded for such a cliche, coincidental plot line. Its too convenient of an explanation with no dramatic weight since its already being heavily hinted at. The big reveal would fall flat since the writers are already leading the audience to it being David. Not to mention that David has a list of girls he went to school with that he wanted punished, what are the odds that theyre all at some festival? Why would that be the place he goes after them even if they were? How would he find them all rather than just targeting them at school?

The *belief* that David is the shooter is enough of a lesson for Robbie.

I do think David will show up again but as someone who went there to help. The piece of evidence that links him to the festival is intentionally vague. His phone could have pinged near the festival because he was nearby, heard the shots, and drove in to pick up victims and bring them to the hospital. It would be an actual subversion of expectations rather than a cliche end to a very improbable series of coincidences.